The present invention provides a melt transesterification process for the production of polycarbonates.
The production of aromatic polycarbonates using the melt transesterification process is known from the literature and is described, for example, in Encyclopedia of Polymer Science, volume 10 (1969), Chemistry and Physics of Polycarbonates, Polymer Reviews, H. Schnell, volume 9, John Wiley and Sons Inc. (1964) and, on the basis of DE 1 031 512, described in various patents. Pat. EP 360 578demonstrates that the end groups of a polycarbonate which has been produced by melt transesterification may be exchanged by addition of a chain terminator. It has, however, been found that only a proportion of the introduced quantity of chain terminator actually remains as an end group in the polycarbonate. Since the end groups have a substantial influence upon mechanical properties, in particular of grades of PC having an elevated chain terminator content, in particular low molecular weight and branched grades of PC, it is desirable to ensure that the phenol end groups are replaced as completely as possible by other more suitable phenols. Moreover, when the phenol arising during polycondensation is removed from the process by distillation, it is contaminated by the chain terminator if this latter substance has not been completely incorporated. It is accordingly desirable to ensure maximally complete incorporation not only with regard to an elevated reaction yield, but also with regard to reuse of the phenol removed by distillation.
The object accordingly arose of providing a melt transesterification process which permits the production of polycarbonates, some of the end groups of which consist of phenols other than phenol, wherein as much of the introduced chain terminator as possible should be incorporated.
This object is achieved by a process for the production of polycarbonates from bisphenols, preferably from bisphenol A, and carbonic acid diesters, in the presence of a phenol suitable as a chain terminator, wherein the phenol used as chain terminator may be introduced in free form or as a compound transesterifiable under the conditions of synthesis, which process is characterised in that phosphonium salts, optionally combined with other catalysts, in particular sodium ions, are used as the catalyst.
For the purposes of the process according to the invention, phosphonium salts are those of the formula (I), 
wherein R1-4 may be identical or different C1-C18 alkyls, C6-C14 aryls, C7-C12 aralkyls or C5-C6cycloalkyls, preferably methyl or C6-C14 aryls, particularly preferably methyl or phenyl, and Xxe2x88x92 may be an anion such as sulfate, hydrogen sulfate, hydrogen carbonate, carbonate, acetate, hydridoborate, hydrogen phosphate, a halide, preferably fluoride, chloride or bromide, an alkoxide of the formula OR, wherein R is C6-C14 aryl, C7-C12 aralkyl, preferably phenyl. Preferred catalysts are
tetraphenylphosphonium fluoride
tetraphenylphosphonium tetraphenylhydridoborate,
particularly preferably tetraphenylphosphonium phenolate.
Sodium ion catalysts which may be used are hydroxides, hydrogen carbonates, carbonates, alkoxides, acetates, hydridoborates, hydrogen phosphates and hydrides, preferably hydroxides and alkoxides, particularly preferably the sodium salts of the phenols and bisphenols as mentioned in relation to the bisphenols and chain terminators and the sodium salt of phenol itself, very particularly preferably the sodium salt of 2,2-bis-(4-hydroxyphenyl)propane.
Alkylphenols suitable as chain terminators for the purposes of the process according to the invention are those of the formula (II), 
wherein R, Rxe2x80x2 and Rxe2x80x3 may mutually independently comprise H, optionally branched C1-C34 alkyl/cycloalkyl, C7-C34 alkaryl or C6-C34 aryl, for example
o-n-butylphenol, m-n-butylphenol, p-n-butylphenol,
o-isobutylphenol, m-isobutylphenol, p-isobutylphenol,
o-tert.-butylphenol, m-tert.-butylphenol, p-tert.-butylphenol,
o-n-pentylphenol, m-n-pentylphenol, p-n-pentylphenol,
o-n-hexylphenol, m-n-hexylphenol, p-n-hexylphenol,
o-cyclohexylphenol, m-cyclohexylphenol, p-cyclohexylphenol,
o-phenylphenol, m-phenylphenol, p-phenylphenol,
o-isooctylphenol, m-isooctylphenol, p-isooctylphenol,
o-n-nonylphenol, m-n-nonylphenol, p-n-nonylphenol,
o-cumylphenol, m-cumylphenol, p-cumylphenol,
o-naphthylphenol, m-naphthylphenol, p-naphthylphenol,
2,5-di-tert.-butylphenol, 2,4-di.-tert.-butylphenol, 3,5-di-tert.-butylphenol,
2,5-dicumylphenol, 3,5-dicumylphenol,
4-phenoxyphenol, 2-phenoxyphenol, 3-phenoxyphenol,
3-pentadecylphenol, 2-pentadecylphenol, 4-pentadecylphenol,
2-phenylphenol, 3-phenylphenol, 4-phenylphenol,
tritylphenol, 3-triphenylmethylphenol, 2-triphenylmethylphenol,
as well as benzotriazole derivatives of the general formula (III) 
with the above-stated meaning of R, Rxe2x80x2 and Rxe2x80x3 for Ra-Rf and chromane compounds such as 
preferably low-boiling phenols such as tritylphenol, cumylphenol, phenoxyphenol, pentadecylphenol or chromanes,
or also as compounds transesterifiable under the conditions of synthesis, such as for example carbonates, oxalates, o-carboxylic acid esters or the like, with preferred compounds being free phenols or carbonic acid diesters of the formula (IV) 
and the formula (V), 
wherein R, Rxe2x80x2 and Rxe2x80x3 correspond to those of the formula (II). Phenols or transesterifiable substances may be added to the synthesis individually or as a mixture. Preferred mixtures are those including diphenyl carbonate. Using the process according to the invention, it is possible to add the phenol or phenol-bearing compound at any time during the reaction, preferably at the beginning of the reaction, and addition may be divided into two or more portions. The entire proportion of carbonic acid esters is 100-130 mol %, preferably 103-120 mol %, relative to the dihydroxy compound.
When producing polycarbonates using the process according to the invention, the chain terminator is preferably added as an alkylphenol at a rate of 0.4-17 mol %, preferably of 1.3-8.6 mol % (relative to the dihydroxy compound). This addition may be made not only before the reaction but also entirely or in part during the reaction.
Dihydroxy compounds for the purposes of the process according to the invention are those of the formula (VI)
HOxe2x80x94Zxe2x80x94OHxe2x80x83xe2x80x83(VI)
in which Z is an aromatic residue having 6 to 30 C atoms, which residue may contain one or more aromatic rings, may be substituted and may contain aliphatic or cycloaliphatic residues or alkylaryls or heteroatoms as linking members.
Examples of dihydroxy compounds of the formula (VI) are
hydroquinone,
resorcinol,
dihydroxydiphenyls,
bis-(hydroxyphenyl)alkanes,
bis-(hydroxyphenyl)cycloalkanes,
bis-(hydroxyphenyl) sulfides,
bis-(hydroxyphenyl) ethers,
bis-(hydroxyphenyl) ketones,
bis-(hydroxyphenyl) sulfones,
bis-(hydroxyphenyl) sulfoxides,
xcex1,xcex1xe2x80x2-bis-(hydroxyphenyl)diisopropylbenzenes
together with the ring-alkylated and ring-halogenated compounds thereof.
These and further suitable other diphenols are described, for example, in U.S. Pat. Nos. 3 028 365, 3 148 172, 3 275 601, 2 991 273, 3 271 367, 3 062 781, 2 970 131 and 2 999 846, in DE-OS 1 570 703, DE-OS 2 063 050, DE-OS 2 063 052, DE-OS 2 211 0956, French patent 1 561 518 and in the monograph by H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964.
Preferred diphenols are, for example:
4,4xe2x80x2-dihydroxydiphenyl,
2,2-bis-(4-hydroxyphenyl)propane,
2,4-bis-(4-hydroxyphenyl)-2-methylbutane,
1,1-bis-(4-hydroxyphenyl)cyclohexane,
1,1-bis-(4-hydroxyphenyl)-4-methylcyclohexane,
xcex1,xcex1xe2x80x2-bis-(4-hydroxyphenyl)-p-diisopropylbenzene,
xcex1,xcex1xe2x80x2-bis-(4-hydroxyphenyl)-m-diisopropylbenzene,
bis-(4-hydroxyphenyl) sulfone,
bis-(4-hydroxyphenyl)methane,
1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,
2,2-bis-(2,6-dimethyl-4-hydroxyphenyl)propane,
2,2-bis-(4-hydroxyphenyl)hexafluoropropane,
1,1-(4-hydroxyphenyl)-1-phenylethane,
bis-(4-hydroxyphenyl)diphenylmethane,
dihydroxydiphenyl ether,
4,4xe2x80x2-thiobisphenol,
1,1-bis-(4-hydroxyphenyl)-1-(1-naphthyl)ethane,
1,1-bis-(4-hydroxyphenyl)-1-(2-naphthyl)ethane,
2,3-dihydroxy-3-(4-hydroxyphenyl)-1,1,3-trimethyl-1H-indene-5-ol,
2,3-dihydroxy-1-(4-hydroxyphenyl)-1,3,3-trimethyl-1H-indene-5-ol,
2,2xe2x80x2,3,3xe2x80x2-tetrahydro-3,3,3xe2x80x2,3xe2x80x2-tetramethyl-1,1xe2x80x2-spirobi[1H-indene]-5,5xe2x80x2-diol.
Particularly preferred compounds are resorcinol,
1,1-bis-(4-hydroxyphenyl)-1-(1-naphthyl)ethane,
1,1-bis-(4-hydroxyphenyl)-1-(2-naphthyl)ethane,
2,2-bis-(4-hydroxyphenyl)propane,
xcex1,xcex1xe2x80x2-bis-(4-hydroxyphenyl)-p-diisopropylbenzene,
xcex1,xcex1xe2x80x2-bis-(4-hydroxyphenyl)-m-diisopropylbenzene,
1,1-bis-(4-hydroxyphenyl)cyclohexane,
1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,
bis-(4-hydroxyphenyl)diphenylmethane,
4,4xe2x80x2-dihydroxydiphenyl.
It is possible both to use one diphenol of the formula (VI), resulting in the formation of homopolycarbonates, and to use two or more diphenols of the formula (VI), resulting in the formation of copolycarbonates.
In the process according to the invention, it is furthermore possible also to add branching agents at a rate of 0.02 to 3.6 mol % (relative to the dihydroxy compound). Suitable branching agents are the compounds suitable for polycarbonate production having three and more functional groups, preferably those having three or more than three phenolic OH groups. Examples of suitable branching agents are
phloroglucinol,
4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)heptane,
1,3,5-tri-(4-hydroxyphenyl)benzene,
1,1,1-tri-(4-hydroxyphenyl)ethane,
tri-(4-hydroxyphenyl)phenylmethane,
2,2-bis-[4,4-bis(4-hydroxyphenyl)cyclohexyl]propane,
2,4-bis-(4-hydroxyphenylisopropyl)phenol,
2,6-bis-(2-hydroxy-5-methylbenzyl)-4-methylphenol,
2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)propane,
hexa-[4-(4-hydroxyphenylisopropyl)phenyl]orthoterephthalic acid ester,
tetra-(4-hydroxyphenyl)methane,
tetra-[4-(4-hydroxyphenylisopropyl)phenoxy]methane,
1,4-bis-[4xe2x80x2,4xe2x80x3-dihydroxytriphenyl)methyl]benzene,
xcex1,xcex1xe2x80x2,xcex1xe2x80x3-tris-(4-hydroxyphenyl)-1,3,4-triisopropenylbenzene,
isatin biscresol,
pentaerythritol,
2,4-dihydroxybenzoic acid,
trimesic acid,
cyanuric acid.
1,1,1-Tri-(4-hydroxyphenyl)ethane and isatin biscresol are particularly preferred.
The process according to the invention is generally performed at temperatures of between 75xc2x0 C. and 325xc2x0 C. and pressures of 1 bar to 0.01 mbar.
The process according to the invention is, for example, performed by, in the first stage, melting the diphenols, carbonic acid diesters and catalyst and optionally the alkylphenols and branching agents at temperatures of 75xc2x0 C. to 225xc2x0 C., preferably of 105xc2x0 C. to 235xc2x0 C., particularly preferably of 120xc2x0 C. to 190xc2x0 C., under standard pressure in 0.1 to 5hours, preferably on 0.25 to 3 hours. Then the oligocarbonate is produced by distilling off the monophenol by applying a vacuum and increasing the temperature. In the final step, the polycarbonate is produced by polycondensation by further increasing the temperature to 240xc2x0 C. to 325xc2x0 C. at a pressure of  less than 2 mbar.
The process according to the invention may be performed both continuously and discontinuously, specifically, for example, in stirred tanks, thin film evaporators, stirred tanks connected in series, extruders, kneaders, simple disk reactors or high viscosity reactors.
The polycarbonates obtainable according to the invention are isolated, for example, by discharging, spinning and pelletising.
The polycarbonates obtainable using the process according to the invention may have weight average molecular weights MW of between approx. 2000 and 150000, preferably of between approx. 4500 and 55000, wherein MW is determined from relative solution viscosity in dichloromethane or in mixtures of identical quantities by weight of phenol/o-dichlorobenzene, wherein calibration is performed by light scattering.
The polycarbonates obtainable according to the invention exhibit the conventional OH end group contents known from the literature, which may be determined photometrically with titanium tetrachloride.
The polycarbonates produced using the process according to the invention exhibit good mechanical properties, elevated transparency and contain no solvents.
Incorporation of the introduced alkylphenols is determined in the case of cumylphenol by 13C-NMR spectroscopy, in the case of other alkylphenols by 1H-NMR spectroscopy. On this basis, the percentage of the introduced chain terminator present as an end group in the polycarbonate was calculated.
The properties of the polycarbonates produced according to the invention may be improved by adding auxiliary substances and reinforcing materials. Such substances and materials which may, inter alia, be considered are: stabilisers, flow auxiliaries, mould release agents, flame retardants, pigments, finely divided minerals, fibrous materials, heat stabilisers, such as for example alkyl and aryl phosphites, phosphates, phosphanes, low molecular weight carboxylic acid esters, halogen compounds, salts, chalk, silica flour, glass and carbon fibres, pigments and combinations thereof.
Other polymers, for example polyolefins, polyurethanes, polyesters and polystyrene, may also be mixed into the polycarbonates according to the invention.
These substances are preferably added to the finished polycarbonate in conventional apparatus, but, if required, may be added at another stage of the process according to the invention.
The polycarbonates obtainable using the process according to the invention may be processed in conventional machinery, for example in extruders or injection moulding machines, using conventional methods to form any desired mouldings, for example to form films or sheets.
These polycarbonate mouldings may be used industrially, for example, in optical and electrical engineering applications.